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author | Jan Kara <jack@suse.cz> | 2011-06-24 23:11:59 +0200 |
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committer | Jan Kara <jack@suse.cz> | 2011-06-27 11:44:37 +0200 |
commit | bb189247f35688a3353545902c56290fb7d7754a (patch) | |
tree | 02f93da7f642f3e59050d1c2837a7a8a8e61b3aa /fs/jbd/transaction.c | |
parent | 2c2ea9451fc2a12ee57c8346f0da26969d07ee7f (diff) | |
download | linux-bb189247f35688a3353545902c56290fb7d7754a.tar.gz linux-bb189247f35688a3353545902c56290fb7d7754a.tar.bz2 linux-bb189247f35688a3353545902c56290fb7d7754a.zip |
jbd: Fix oops in journal_remove_journal_head()
journal_remove_journal_head() can oops when trying to access journal_head
returned by bh2jh(). This is caused for example by the following race:
TASK1 TASK2
journal_commit_transaction()
...
processing t_forget list
__journal_refile_buffer(jh);
if (!jh->b_transaction) {
jbd_unlock_bh_state(bh);
journal_try_to_free_buffers()
journal_grab_journal_head(bh)
jbd_lock_bh_state(bh)
__journal_try_to_free_buffer()
journal_put_journal_head(jh)
journal_remove_journal_head(bh);
journal_put_journal_head() in TASK2 sees that b_jcount == 0 and buffer is not
part of any transaction and thus frees journal_head before TASK1 gets to doing
so. Note that even buffer_head can be released by try_to_free_buffers() after
journal_put_journal_head() which adds even larger opportunity for oops (but I
didn't see this happen in reality).
Fix the problem by making transactions hold their own journal_head reference
(in b_jcount). That way we don't have to remove journal_head explicitely via
journal_remove_journal_head() and instead just remove journal_head when
b_jcount drops to zero. The result of this is that [__]journal_refile_buffer(),
[__]journal_unfile_buffer(), and __journal_remove_checkpoint() can free
journal_head which needs modification of a few callers. Also we have to be
careful because once journal_head is removed, buffer_head might be freed as
well. So we have to get our own buffer_head reference where it matters.
Signed-off-by: Jan Kara <jack@suse.cz>
Diffstat (limited to 'fs/jbd/transaction.c')
-rw-r--r-- | fs/jbd/transaction.c | 73 |
1 files changed, 37 insertions, 36 deletions
diff --git a/fs/jbd/transaction.c b/fs/jbd/transaction.c index dc39efd05d54..7e59c6e66f9b 100644 --- a/fs/jbd/transaction.c +++ b/fs/jbd/transaction.c @@ -696,7 +696,6 @@ repeat: if (!jh->b_transaction) { JBUFFER_TRACE(jh, "no transaction"); J_ASSERT_JH(jh, !jh->b_next_transaction); - jh->b_transaction = transaction; JBUFFER_TRACE(jh, "file as BJ_Reserved"); spin_lock(&journal->j_list_lock); __journal_file_buffer(jh, transaction, BJ_Reserved); @@ -818,7 +817,6 @@ int journal_get_create_access(handle_t *handle, struct buffer_head *bh) * committed and so it's safe to clear the dirty bit. */ clear_buffer_dirty(jh2bh(jh)); - jh->b_transaction = transaction; /* first access by this transaction */ jh->b_modified = 0; @@ -1069,8 +1067,9 @@ int journal_dirty_data(handle_t *handle, struct buffer_head *bh) ret = -EIO; goto no_journal; } - - if (jh->b_transaction != NULL) { + /* We might have slept so buffer could be refiled now */ + if (jh->b_transaction != NULL && + jh->b_transaction != handle->h_transaction) { JBUFFER_TRACE(jh, "unfile from commit"); __journal_temp_unlink_buffer(jh); /* It still points to the committing @@ -1091,8 +1090,6 @@ int journal_dirty_data(handle_t *handle, struct buffer_head *bh) if (jh->b_jlist != BJ_SyncData && jh->b_jlist != BJ_Locked) { JBUFFER_TRACE(jh, "not on correct data list: unfile"); J_ASSERT_JH(jh, jh->b_jlist != BJ_Shadow); - __journal_temp_unlink_buffer(jh); - jh->b_transaction = handle->h_transaction; JBUFFER_TRACE(jh, "file as data"); __journal_file_buffer(jh, handle->h_transaction, BJ_SyncData); @@ -1300,8 +1297,6 @@ int journal_forget (handle_t *handle, struct buffer_head *bh) __journal_file_buffer(jh, transaction, BJ_Forget); } else { __journal_unfile_buffer(jh); - journal_remove_journal_head(bh); - __brelse(bh); if (!buffer_jbd(bh)) { spin_unlock(&journal->j_list_lock); jbd_unlock_bh_state(bh); @@ -1622,19 +1617,32 @@ static void __journal_temp_unlink_buffer(struct journal_head *jh) mark_buffer_dirty(bh); /* Expose it to the VM */ } +/* + * Remove buffer from all transactions. + * + * Called with bh_state lock and j_list_lock + * + * jh and bh may be already freed when this function returns. + */ void __journal_unfile_buffer(struct journal_head *jh) { __journal_temp_unlink_buffer(jh); jh->b_transaction = NULL; + journal_put_journal_head(jh); } void journal_unfile_buffer(journal_t *journal, struct journal_head *jh) { - jbd_lock_bh_state(jh2bh(jh)); + struct buffer_head *bh = jh2bh(jh); + + /* Get reference so that buffer cannot be freed before we unlock it */ + get_bh(bh); + jbd_lock_bh_state(bh); spin_lock(&journal->j_list_lock); __journal_unfile_buffer(jh); spin_unlock(&journal->j_list_lock); - jbd_unlock_bh_state(jh2bh(jh)); + jbd_unlock_bh_state(bh); + __brelse(bh); } /* @@ -1661,16 +1669,12 @@ __journal_try_to_free_buffer(journal_t *journal, struct buffer_head *bh) /* A written-back ordered data buffer */ JBUFFER_TRACE(jh, "release data"); __journal_unfile_buffer(jh); - journal_remove_journal_head(bh); - __brelse(bh); } } else if (jh->b_cp_transaction != NULL && jh->b_transaction == NULL) { /* written-back checkpointed metadata buffer */ if (jh->b_jlist == BJ_None) { JBUFFER_TRACE(jh, "remove from checkpoint list"); __journal_remove_checkpoint(jh); - journal_remove_journal_head(bh); - __brelse(bh); } } spin_unlock(&journal->j_list_lock); @@ -1733,7 +1737,7 @@ int journal_try_to_free_buffers(journal_t *journal, /* * We take our own ref against the journal_head here to avoid * having to add tons of locking around each instance of - * journal_remove_journal_head() and journal_put_journal_head(). + * journal_put_journal_head(). */ jh = journal_grab_journal_head(bh); if (!jh) @@ -1770,10 +1774,9 @@ static int __dispose_buffer(struct journal_head *jh, transaction_t *transaction) int may_free = 1; struct buffer_head *bh = jh2bh(jh); - __journal_unfile_buffer(jh); - if (jh->b_cp_transaction) { JBUFFER_TRACE(jh, "on running+cp transaction"); + __journal_temp_unlink_buffer(jh); /* * We don't want to write the buffer anymore, clear the * bit so that we don't confuse checks in @@ -1784,8 +1787,7 @@ static int __dispose_buffer(struct journal_head *jh, transaction_t *transaction) may_free = 0; } else { JBUFFER_TRACE(jh, "on running transaction"); - journal_remove_journal_head(bh); - __brelse(bh); + __journal_unfile_buffer(jh); } return may_free; } @@ -2070,6 +2072,8 @@ void __journal_file_buffer(struct journal_head *jh, if (jh->b_transaction) __journal_temp_unlink_buffer(jh); + else + journal_grab_journal_head(bh); jh->b_transaction = transaction; switch (jlist) { @@ -2127,9 +2131,10 @@ void journal_file_buffer(struct journal_head *jh, * already started to be used by a subsequent transaction, refile the * buffer on that transaction's metadata list. * - * Called under journal->j_list_lock - * + * Called under j_list_lock * Called under jbd_lock_bh_state(jh2bh(jh)) + * + * jh and bh may be already free when this function returns */ void __journal_refile_buffer(struct journal_head *jh) { @@ -2153,6 +2158,11 @@ void __journal_refile_buffer(struct journal_head *jh) was_dirty = test_clear_buffer_jbddirty(bh); __journal_temp_unlink_buffer(jh); + /* + * We set b_transaction here because b_next_transaction will inherit + * our jh reference and thus __journal_file_buffer() must not take a + * new one. + */ jh->b_transaction = jh->b_next_transaction; jh->b_next_transaction = NULL; if (buffer_freed(bh)) @@ -2169,30 +2179,21 @@ void __journal_refile_buffer(struct journal_head *jh) } /* - * For the unlocked version of this call, also make sure that any - * hanging journal_head is cleaned up if necessary. - * - * __journal_refile_buffer is usually called as part of a single locked - * operation on a buffer_head, in which the caller is probably going to - * be hooking the journal_head onto other lists. In that case it is up - * to the caller to remove the journal_head if necessary. For the - * unlocked journal_refile_buffer call, the caller isn't going to be - * doing anything else to the buffer so we need to do the cleanup - * ourselves to avoid a jh leak. - * - * *** The journal_head may be freed by this call! *** + * __journal_refile_buffer() with necessary locking added. We take our bh + * reference so that we can safely unlock bh. + * + * The jh and bh may be freed by this call. */ void journal_refile_buffer(journal_t *journal, struct journal_head *jh) { struct buffer_head *bh = jh2bh(jh); + /* Get reference so that buffer cannot be freed before we unlock it */ + get_bh(bh); jbd_lock_bh_state(bh); spin_lock(&journal->j_list_lock); - __journal_refile_buffer(jh); jbd_unlock_bh_state(bh); - journal_remove_journal_head(bh); - spin_unlock(&journal->j_list_lock); __brelse(bh); } |